ORGANS OF THE BODY. 425 



Around certain single cells, namely, which appear not unfrequently to 

 be undergoing fatty metamorphosis, or again, about a group of the latter, 

 we notice the formation of dense concentric layers, which may be seen on 

 closer examination to be composed of flat nucleated cells, like pavement 

 epithelia (Ecker, Paulitzky], reminding us of the formations in epithelial 

 cancer, so well known to pathologists. 



The smaller examples of these bodies (g) are formed of a group of cells, 

 sometimes filled with granules, sometimes with fatty matter, and in some 

 cases still possessing nuclei ; which is surrounded by the thick laminated 

 rind alluded to ; they may attain a diameter of -01 69-0-0208 mm. The 

 larger structures of this kind (h), measuring 0-0593 mm., are formed by a 

 repetition of the process enclosing several of these smaller corpuscles. 



As regards the lymphatics of the thymus, we are still comparatively 

 ignorant. That the chief stems accompany the arteries and veins through 

 the central band, has been already remarked above ; but besides these 

 there are finer lymphatic vessels to be seen. These are found in the 

 interstitial connective- tissue of the lobes, according to His, in the form of 

 delicately walled tubes, only coursing round the latter. They are even 

 stated by that observer to open into passages about 0'0226 mm. in 

 breadth, filled with lymphoid cells, which spring from the centre of the 

 acinus. Through these tubes a communication exists, according to His, 

 between the central cavity and the lymphatic vessels, by means of which 

 the cellular elements can pass into the latter. 



From the fact, however, that up to the present no one has succeeded, 

 by puncture, in filling lymphatic vessels around the acini of the thymus, 

 (and my own numerous experiments also teach me that it cannot be done) ; 

 and as the discoveries of more recent date, relating to lymphoid organs, 

 do not seem favourable to the supposition of such an arrangement of parts 

 as His describes, the matter would seem to call for closer investigation. 



The final distribution of nerves in this organ is still enveloped in 

 obscurity. 



As to the composition of the thymus (whose specific gravity is stated 

 at 1 '046 by Krause and Fischer), analyses have been made by Simon and 

 Friedleben. The former of these obtained from the organ of a calf three 

 months old, about 77 per cent, of water, circa 4 of an albuminous sub- 

 stance, traces of fat and 2 per cent, of salts. 



The thymus ef the calf is further stated by Gorup, Frerichs, Staedeler, 

 and Scherer, to contain large quantities of leucin, also hypoxanthin and 

 xanthin, volatile fatty acids, such as acetic and formic ; also succinic and 

 lactic acids. The mineral constituents consist principally of phosphates 

 and chlorides of the alkalies, with a preponderance of phosphoric acid and 

 soda. The proportion likewise of the magnesian exceeds that of the lime 

 salts. Sulphuric acid is only present in small traces. The presence of 

 salts of ammonia is a fact of some interest (Frerichs arid Staedeler). On 

 the whole, its composition has some resemblance to that of muscle. 



The development of the thymus was first explained by Simon, whose 

 statements were subsequently corroborated by Ecker. 



In the mammal, as far as has up to the present been ascertained, it 

 appears first in the form of an elongated and closed sac lying in front of 

 the carotids, which is filled with cells and granular contents. By a 

 bulging of the walls of this, numerous rounded prominences are formed, 

 in which we have the first indication of the future lobes. By a repetition 

 of the process the capsule of the glands is eventually formed. A subse- 



